For the purposes of this act, limited access highways are defined as highways specially designed for through traffic, and over, from or to which owners or occupants of abutting land have no easement or right of light, air or access by reason of such abuttal. Such highways may be parkways, with or without landscaped roadsides, from which trucks, buses and other commercial vehicles are excluded; or they may be motorways open to use by all common forms of highway traffic.